<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .page_header {
            font-size: 28px;
        }

        .item {
            width: 70px;
            height: 30px;
            margin: 5px;
            border: 1px solid green;
            display: inline-block;
        }
    </style>
</head>

<body>
    <div class="container">
        <h2 class="page_header">点击切换颜色</h2>
        <div class="item"></div>
        <div class="item"></div>
        <div class="item"></div>
    </div>

    <script>
        let items = document.getElementsByClassName('item');
        for (let i = 0; i < items.length; i++) {
            items[i].onclick = function () {
                this.style.background = 'pink';
            }
        }
    </script>
</body>

</html>